Heretofore, as disclosed in the following Patent Document 1, there has been known an automatic transmission speed change control apparatus equipped with an oil temperature sensor for detecting a temperature of oil for engaging a frictional engagement unit of an automatic transmission, and adapted to prohibit a specific speed change when a temperature of the oil detected by the oil sensor is equal to or less than a predetermined reference temperature, wherein the speed change control apparatus comprises: failure detection means operable to detect an abnormality of the oil temperature sensor; oil temperature estimation means operable, when an abnormality of the oil temperature sensor is detected, to estimate a temperature of the oil; and prohibition control means operable, when the estimated temperature of the oil is equal to or less than the reference temperature, to prohibit the specific speed change, and, when the estimated temperature of the oil is greater than the reference temperature, to release the prohibition of the specific speed change, whereby it becomes possible to prevent worsening of speed change shock and deterioration in durability of the frictional engagement unit, in the event of failure of the oil temperature sensor.
Further, as disclosed in the following Patent Document 2, there has been known an automatic transmission control unit thermal runaway preventive apparatus for preventing runaway of an automatic transmission control unit under a high temperature equal to or greater than a given value, wherein the thermal runaway preventive apparatus comprises temperature monitoring means operable, when a temperature detected in or around the automatic transmission control unit is equal to or greater than a predetermined first temperature, to temporarily stop a function of the automatic transmission control unit until the detected temperature is lowered to be less than the first temperature or greater than the first temperature by a value corresponding to hysteresis, and, when the detected temperature is equal to or greater than a predetermined second temperature greater than the first temperature, to completely stop the function of the automatic transmission control unit even after the detected temperature is lowered to be less than the second temperature, whereby it becomes possible to prevent runaway of the automatic transmission control unit when it is disposed in an environment where a temperature change is more likely to occur.